Zingerone in the floral synomone of Bulbophyllum baileyi (Orchidaceae) attracts Bactrocera fruit flies during pollination

Many orchids use specific volatile chemical(s) in floral fragrance to attract potential pollinators to locate and visit flowers in the tropical rain forests. Male fruit flies (Bactrocera species) are attracted to the ‘fruity odour’ of Bulbophyllum baileyi. The floral chemical component responsible for this fruit fly attraction is zingerone, which also acts as a floral chemical reward during pollination. Zingerone (5 mg), absorbed into a filter and released via a portable-battery operated fan between 0900 and 1100 h, attracted 5–7 males of Bactrocera indonesiae in an orchard located in Kedah, Malaysia. In Penang island, the fruit fly species attracted are Bactrocera dorsalis (methyl eugenol-sensitive) and Bactrocera albistragata (raspberry ketone-sensitive). An attracted male fruit fly probes and feeds on floral petal or sepal before climbing on to the small see-saw lip (labellum). While on the lip and due to shifting of the fly's weight, the fly is toppled head first into the column cavity and simultaneously touches and consequently gets stuck to the sticky viscidium of pollinarium that still remained in the anther. It spends 23–46 min trying to free itself from being suspended from the floral column. Removal of pollinarium (pollinia, stipe and viscidium) is a long process. A male B. dorsalis that fed on a B. baileyi flower was found to sequester zingerol (a reduced form of zingerone) in the body, suggesting its role as sex pheromone to attract a female during courtship behaviour.